User- and Process-Driven
Dynamic Voltage and Frequency Scaling
Bin Lin
Arindam Mallik
Peter Dinda
Gokhan Memik
Robert Dick
Empathic Systems Project
Department of Electrical Engineering and Computer Science
Northwestern University
http://empathicsystems.org
Summary
• User-Driven Frequency Scaling (UDFS)
– Adjust CPU frequency according to satisfaction
of individual user, exploiting variation in
satisfaction among users
• Process-Driven Voltage Scaling (PDVS)
– Adjust voltage at frequency and temperature
based on profile of the individual processor,
exploiting variation among processors
• ~50% power reduction on Windows tasks
compared to Windows DVFS
– User study, measured system power
2
Outline
• Summary
• User-Driven frequency scaling (UDFS)
– User pessimism study
– UDFS2 algorithm
• Process-Driven voltage scaling (PDVS)
– PDVS profiling
• Evaluation of UDFS and PDVS
• Work in context
• Conclusion
3
User Satisfaction With CPU Frequency
• How satisfied are users of different applications
at different clock frequencies?
• Earlier work suggests there will much variation
• User Study
– 8 users
– 3 frequencies + Windows XP DVFS
– 3 typical Windows apps
• Presentation, Animation, Game
– Rate comfort on Leikert-like 1 to 10 scale
4
Presentation
• Dramatic
variation in user
satisfaction for
fixed frequencies
– And for DVFS
Game
• Setting
frequency for
worse case user
is pessimistic
• Setting it for an
“average” user is
5
also wrong
User-Driven Frequency Scaling (UDFS)
• Developed system to dynamically customize
frequency to the individual user
– Key idea: user feedback at run-time
– User presses “irritation button” (F11) as input
• But not too often!
– 2 very simple learning algorithms
• UDFS1, UDFS2
6
UDFS2 Algorithm
• Goal: probe to find the lowest frequency
level the user is comfortable at and
stabilize there
• General idea: react additively to both
passage of time and user irritation
events; also update rate of reaction
based on rate of user feedback
– UDSF1, in contrast, is an additive
increase/multiplicative decrease algorithm,
analogous to TCP Reno congestion control
7
UDFS2 Algorithm
• Each frequency level ri has interval ti
– ti = 10 seconds, initially
– ri are frequencies in descending order
• User not irritated in current interval ti ?
– Switch frequency to ri+1 , interval ti+1
• Let’s go slower in the next interval
8
UDFS2 Algorithm
• User irritated in current interval ti ?
– ti-1 = a ti-1
(a>1)
• We should spend more time at the next highest
frequency
– tk = b tk " k: ki-1 (b<1)
• We should spend less time at the other
frequencies, including this one
– Switch frequency to ri-1 , interval ti-1
 a = 2.5, b=0.8 in our studies
9
UDFS2 in Action
(User is playing a game)
Note Convergence
10
Outline
• Summary
• User-Driven frequency scaling (UDFS)
– User pessimism study
– UDFS2 algorithm
• Process-Driven voltage scaling (PDVS)
– PDVS profiling
• Evaluation of UDFS and PDVS
• Work in context
• Conclusion
11
CPU Voltage
• Minimum voltage needed for CPU
stability is a function of frequency and
temperature
• Claim: function varies across individual
parts for many interesting processors
• Hence, we can do better than the worst
case (nominal) function
– P  V2CF makes even small changes
significant
12
Example
This processor can be run at lower
voltages than specifications indicate 13
2.13 GHz Pentium M-770 in a Thinkpad T43p
Process-Driven Voltage Scaling
• Profiling System (Boot CD)
–
–
–
–
–
Workload generator
Temperature monitor
Frequency selector
Voltage selector
Watchdog timer
• For each frequency/temperature
– Modulate workload to maintain
temperature
Profile:
– Decrease voltage until watchdog timer
min_voltage(frequency, temperature)
fires and reboots machine
Any DVFS Scheme
• Profiling system implemented by
Nikolay Valtchanov and Matt Robben
14
Outline
• Summary
• User-Driven frequency scaling (UDFS)
– User pessimism study
– UDFS2 algorithm
• Process-Driven voltage scaling (PDVS)
– PDVS profiling
• Evaluation of UDFS and PDVS
• Work in context
• Conclusion
15
Experimental Setup
• IBM Thinkpad T43p
– 2.13 GHz Pentium M-770
– 1 GB RAM
– Windows XP SP2
• UDFS system (or Windows DVFS) runs online,
adjusting CPU frequency as user interacts with the
system and applications
• PDVS effects and power measurements/analysis are
done offline, using logs from UDFS and user traces
– System power measurement
– CPU dynamic power via simulation
16
Application Tasks
• Use Microsoft Powerpoint 2003 to
replicate a presentation while listening
to background music with Windows
Media Player 10
• Watch 3D Shockwave animation with
Microsoft Internet Explorer (locally
stored animation)
• Play FIFA 2005 Soccer (first person
shooter game)
17
Users
• 20 participants recruited from Northwestern
population via IRB-approved methods
• Participants self-identified as “Power User”, “Typical
User”, “Beginner” for each application, plus PCs and
Windows
• A demographic mix
18
Study Process
• Fill out a questionnaire (2 minutes)
• Read a one page handout (2 minutes)
• Acclimatize to the performance of our
machine by using the apps (5 minutes)
• Perform the following tasks for UDFS1
– Powerpoint (4 minutes)
– 3D Shockwave (4 minutes)
– FIFA game (8 minutes)
• Repeat previous for UDFS2
19
Results
Compared to Windows DVFS Unless Otherwise Noted
• Measured system power
– UDFS1, UDFS2, UDFS1+PDVS,
UDFS2+PDVS, Windows DVFS+PDVS
• Simulated CPU dynamic power
– UDFS1, UDFS2, UDFS1+PDVS,
UDFS2+PDVS, Windows DVFS+PDVS
• Measured mean and peak temperature
– UDFS1, UDFS2, UDFS1+PDVS,
UDFS2+PDVS
• User irritation event rate (UDFS1,2)
• Multitasking study
20
Measured System Power
(PowerPoint, % improvement over Windows DVFS)
PDVS dominates gains for less interactive
applications with little user-user variance 21
Measured System Power
(FIFA, % improvement over Windows DVFS)
UDFS contributes significant gains for
more interactive applications
22
Measured Temperature
(PowerPoint)
Significant temperature reductions are
possible using UDFS and PDVS
23
Measured Temperature
(FIFA Game)
Significant temperature reductions are
possible using UDFS and PDVS
24
User Irritation Button Presses
First 4 minutes
Second 4 minutes
Rate of user feedback can be low, and
can decrease with time
25
Outline
• Summary
• User-Driven frequency scaling (UDFS)
– User pessimism study
– UDFS2 algorithm
• Process-Driven voltage scaling (PDVS)
– PDVS profiling
• Evaluation of UDFS and PDVS
• Work in context
• Conclusion
26
Work In Context of Power Management Efforts in the
Empathic Systems Project (empathicsystems.org)
•
•
•
•
•
•
A. Gupta, B. Lin, P. Dinda, Measuring And Understanding User Comfort With Resource
Borrowing, HPDC 2004
– Opportunity paper: Identification of variance in user satisfaction with systems decisions
P. Dinda, G. Memik, R. Dick, B. Lin, A. Mallik, A. Gupta, S. Rossoff, The User In
Experimental Computer Systems Research, ExpCS 2007
– Position paper: overview of goals of project and advocacy for user-driven work
A. Mallik, J. Cosgrove, R. Dick, G. Memik, P. Dinda, PICSEL: Measuring User-Perceived
Performance to Control Dynamic Frequency Scaling, ASPLOS 2008
– Customize power management to user by observing output to him
A. Shye, B. Ozisikyilmaz, A. Mallik, G. Memik, P. Dinda, R. Dick, A. Choudhary, Learning
and Leveraging the Relationship between Architectural-level Measurements and Individual
User Satisfaction, ISCA 2008
– Learn performance counter->user satisfaction and use in power management
A. Shye, Y. Pan, B. Scholbrock, J. S. Miller, G. Memik, P. Dinda, R. Dick, Power to the
People: Leveraging Human Physiological Traits to Control Microprocessor Frequency,
MICRO 2008
– Measure user satisfaction using biometrics and use in power management
[This paper]
– Direct user feedback for power management + PDVS
27
Related Work
• DVFS in general
– Gochman, et al [Intel Tech Journal], Broch, et al [SOC03],
and many more…
• Dynamic Thermal Management
– Liu, et al [IEEE JSSC-93], Brookes, et al [WCED00], Crusoe,
Intel Pentium-M, etc…
• PDVS-related
– Teodorescu, et al [ISCA08], Razor [Ernst, et al, MICRO03],
Dhar, et al [ISLPED05], Intel Foxton, AutoDVS [EMSOFT05],
etc…
• UDFS-related
– Lorch, et al [UCB TR], Yan, et al [DAC05], Vertigo [OSDI02],
Xu, et al [EMSOFT05], Ranga, et al [IEEE Computer-06],
Anand, et al [MOBICOMM03], Theocharous, et al [Intel Tech
28
Journal 06]
Conclusion
• User-Driven Frequency Scaling (UDFS)
– Adjust CPU frequency according to satisfaction of
individual user, exploiting variation in satisfaction
among users
• Process-Driven Voltage Scaling (PDVS)
– Adjust voltage at frequency and temperature based on
profile of the individual processor, exploiting variation
among processors
• ~50% power reduction on Windows tasks
compared to Windows DVFS
– User study, measured system power
• Variation is opportunity
29
For More
Information
• Empathic Systems Project
– http://empathicsystems.org
• Prescience Lab
– http://presciencelab.org
• Peter Dinda
– http://pdinda.org
30
Measured System Power
(Multitasking Study, % improvement over Windows DVFS))
Multitasking appears to increase benefits
Small additional study where user watched 3D animation while also
listening to MP3s using Windows Media Player
31
Measured System Power
(3D Shockwave, % improvement over Windows DVFS)
UDFS contributes significant gains for
more interactive applications
32
Measured Temperature
(3D Shockwave)
Significant temperature reductions are
possible using UDFS and PDVS
33